Vol 62, No 2 (2017)
- Year: 2017
- Articles: 12
- URL: https://journals.rcsi.science/1064-2269/issue/view/12370
Electrodynamics and Wave Propagation
On the dispersion distortions of a rectangular radio pulse in a resonance absorbing gas medium
Abstract
The possible character and peculiarities of dispersion distortions of a supershort radio pulse are considered on the basis of the analytical description obtained beforehand for the propagation of an electromagnetic pulse in a resonance absorbing medium. The pulse has a rectangular initial form and the carrying frequency coinciding with the resonance frequency of the strongest line characterizing the water vapor absorption in the millimeter wave range.
Spatial distribution of the demodulated low-frequency field in the low-latitude perturbed ionosphere
Abstract
Features of propagation of low-frequency electromagnetic waves in the low-latitude ionosphere are considered in the case when such waves are generated by means of demodulation of the radiation of a high-power short-wave ground transmitter in the lower ionosphere. Calculations are performed in the ray approximation based on a simplified model (developed specially for the case under study) of the anomaly of the low-latitude equatorial electron density. It is demonstrated that latitude gradients of the equatorial anomaly may result in both additional focusing and defocusing of the beam of demodulated low-frequency waves.
Amplifying of surface plasmon-polariton in a metal–gain medium–vacuum structure
Abstract
Propagation of a surface plasmon-polariton in a three-layer system consisting of the half-space filled with a metal, a layer of the gain medium of a finite thickness, and a half-space filled with vacuum is considered. The existence of the optimum thickness of the amplifying layer at which the plasmon is amplified several times stronger than in the case of infinite thickness is demonstrated. In particular, the plasmon loss can be compensated at a lower pumping intensity than in the case of infinite thickness of the gain layer.
Statistical Radiophysics
Synthesis of adaptive tracking systems based on the hypothesis of stationarity of the Hamiltonian on the switching hypersurface
Abstract
Application of the method of the combined maximum principle to the synthesis of filters for tracking maneuvering aircrafts is demonstrated. The derived estimation equations are determined to within the synthesizing function. In constructing this function, the condition of stationarity of the Hamiltonian function on the switching hypersurface is used, which ensures adaptation to the observed motion. A tracking algorithm characterized by a lower, as compared to the Kalman filter, computational complexity and higher estimation accuracy during aircraft maneuvering has been synthesized.
Theory and Methods of Signal Processing
Correlation functions of complete CBOC signals derived as the inverse Fourier transform of energy spectra
Abstract
For the complete composite binary offset carrier (CBOC) signals of new-generation global satellite radio-navigation satellite systems (SRNSs), analytical expressions for correlating functions (CFs) characterizing the single components of the modulating function are derived in terms of the inverse Fourier transform (IFT) of energy spectra at different fractional coefficients. The CF calculation technique is based on the energy spectra of complete CBOC signals represented as a partial sum of the series of cosines of the angles that are multiples of the angle γCBOC = ωτM2, where τM2 is the meander-pulse duration of the subcarrier oscillation of binary offset carrier (BOC) signals with BOC(6,1) modulation. In a number of cases, the IFT of energy spectra applied to calculating the CFs of complete CBOC signals is preferable (in particular, from the viewpoint of labor intensiveness) to the procedures by which CFs are obtained using the general definition. The CFs graphs constructed with the help of complete CBOC signals employed in the E1 band of the Galileo SRNS are presented.
Method for determining the mutual time delay of ultrawideband OFDM signals
Abstract
The efficient algorithm for determining the mutual time delay of orthogonal frequency-division multiplexing (OFDM) signals propagating in ultrawideband (UWB) satellite communications systems is proposed. The algorithm is based on modified calculation of the mutual uncertainty function of signals to compensate for the Doppler effect. The directly calculated mutual uncertainty function of UWB signals makes it impossible to obtain the consistent estimate of the mutual time delay due to the influence of the Doppler broadening of a spectral band. The proposed algorithm relies on the fact that received signals are divided into separate narrowband channels in which mutual uncertainty functions are subsequently calculated. The algorithm operation modes based on OFDM and pseudorandom frequency-hopping signals are compared.
Theory of Radio Circuits
Convergence of Volterra series in simulation of nonlinear processes in electronic circuits
Abstract
Physical and mathematical reasons for the divergence of functional Volterra series in calculation of nonlinear electronic circuits described by algebraic differential equations are considered. It is shown that the main reason is the character of the feedbacks involving nonlinear elements and leading to a high level of repeated combinational interactions. On model examples, the disruption of the iterative process due to the loss of continuity and differentiability of nonlinear operators on the real axis or on the complex plane is demonstrated.
Radio Phenomena in Solids and Plasma
Local development of transmission and reflection of elementary field of stepwise excitation for orthotropic paramagnetic composite
Abstract
A problem of local subsurface probing of an orthotropic paramagnetic composite using a point source of stepwise external current that is parallel to a plane surface is formulated. Multidimensional Laplace–Carson transform is used to obtain transforms of the x (and y) Cartesian projection of the transmission and reflection characteristics. Analytical characteristics are determined at the origin. Expressions for the real and imaginary components of the x (and y) projections of characteristics are derived, the main properties are studied, and the computations are minimized at a predetermined accuracy using the Horner scheme. The relation of main stages and specific moments of the local development of transmission and reflection of elementary field of stepwise excitation is determined for orthotropic paramagnetic composite.
Study of a longitudinally nonuniform plasma layer
Abstract
Transformation of the energy of surface waves in a plane plasma layer with a longitudinal irregularity of density is studied by the method of spectral decomposition. The total field is represented by an expansion in surface and pseudo-surface waves. A system of integro-differential equation for the coefficients of expansion determining the amplitudes of the transmitted, reflected, and scattered waves is obtained. It is shown that, in some special cases, this system of equations is reduced to a system of ordinary differential equations even if the plasma density rapidly changes. The fraction of the energy of surface waves that transforms into radiation at an acute angle with the layer can reach 50–60%.
Luminescence of disordered crystals with langasite structure doped with chromium ions
Abstract
The luminescence, absorption and circular dichroism spectra of langasite family crystals La3Ga5-SiO14 and Sr3Ga2Ge4O14 doped with chromium ions (0.1 at %) are studied in the region of 300–1200 nm. It is demonstrated that these spectra contain bands typical of both a Cr3+ ion in an octahedral environment (position 1a) and a Cr4+ ion in a tetrahedral site (position 2d). The intensities of these bands differ considerably.
Physical Processes in Electron Devices
Switching regimes of compact triggered vacuum gaps
Abstract
Dynamic characteristics of compact vacuum gaps are studied. Experiments are performed in the microsecond range of current pulses with amplitudes ranging from 50 A to 5 kA and rates of rise ranging from 109 to 1010 A/s at switching voltages ranging from 2 to 10 kV. The most stable operation of the gaps is reached when the cathode is triggered using positive pulses. The instability of the initial stage of burning of vacuum arc leads to an increase in the stabilization time of the main discharge. Electrical valve-like properties of compact gaps are manifested in the stable quenching of vacuum arc at a current attenuation rate of 0.5 kA/μs.
Novel Radio Systems and Elements
Planar three-resonator bandpass filters with cross coupling
Abstract
New designs of planar three-resonator bandpass filters with cross coupling having a large variety of frequency characteristics are considered. In addition to better one-sided selectivity, such filters implement symmetric amplitude–frequency characteristics with an attenuation pole at each side of the passband. These filters can also have constant delay time in the passband. Concatenation of the proposed three-resonator filters leads to multiresonator filters with high selectivity determined by two attenuation poles at each side of the passband. It is found that the type of connection of the middle resonator in the circuit of a three-resonator filter with cross coupling results in substantial differences in amplitude–frequency characteristics. The results of modeling of different frequency characteristics are presented. It is shown that filters have small dimensions, which are comparable to overall dimensions of microwave ceramic filters. For example, dimensions of a three-resonator stripline filter designed for a frequency of 1.9 GHz are 9.4 × 5 × 2 mm for the permittivity of the filter material εr = 92 and dimensions of a six-resonator filter are 10 × 9.4 × 2 mm.